<DOCTYPE>
    <html>
    <body>
        <P>点击这个按钮，获得基于时间的问候。</P>
        <button onclick="myFunction()">点击这里</button>
        <p id="demo"></p>
        <script>
        function myFunction()
        {
            var x="";
            var time=new Date().getHours();
            if (time<20)
            {
                x="good day";
            }
            else
            {
                x="good night";
            }
        
         document.getElementById("demo").innerHTML=x;
        }
        </script>
    </body>
    </html>